The present invention relates to a method of data transmission in a restraint system networked over a bus line for occupants of a vehicle, where a central control unit and a plurality of data processing units are connected to the bus line and are provided at various locations in the vehicle to control restraint devices, and the central control unit sends query signals or control signals in the form of data telegrams to all or certain individual data processing units and the data processing units send response signals back to the central control unit in response to given query or control signals.
The efficiency of the restraint systems in vehicles will increase greatly in the future to further improve the protection of passengers in the vehicle. This means that the number of restraint devices and their respective deployment means in the vehicle will increase drastically. These restraint devices will then include, for example, airbags for the driver and front passenger, optionally with multi-stage deployment, knee bags for the driver and front passenger, side airbags for the driver, front passenger and rear passengers, with side airbags possibly being provided for the head area as well as the chest area, seat belt tensioners which may also be activated in multiple stages, possibly also rollover bars, etc. Thus, a complex safety system composed of multiple restraint devices will be installed in the vehicle for each occupant of the vehicle.
A complex restraint system is described in the article xe2x80x9cBussystem zur Vernetzung von Aktuatoren fur Ruckhaltesystemexe2x80x9d [Bus system for networking actuators for restraint systems] by J. Bauer, G. Mehler and W. Nitschke in the Conference Proceedings of the SAE International Congress and Exposition, Feb. 24-27, 1997 Detroit. Bulky wiring harnesses have been eliminated by the introduction of a bus system which networks all the restraint devices. With this conventional system, each restraint device has its own data processing unit having a processing unit, data input and output circuits, a memory unit, a time and clock base and a power supply. This data processing unit, which is also referred to as a peripheral intelligent ignition power module, is arranged in immediate proximity to the deployment means belonging to the respective restraint device, namely, in an ignitor cap or on a substrate of the ignitor itself.
From a central control unit, each data processing unit receives its power supply over a bus line. In addition, the central control unit determines on the basis of multiple sensor signalsxe2x80x94e.g., acceleration sensors, precrash sensors, seat occupancy sensorsxe2x80x94which restraint devices are to be deployed. Accordingly, the central control unit addresses the respective data processing units with the help of a protocol transmitted over the bus line. Diagnostic requests also go out over the bus line from the central control unit to the individual data processing units which send their diagnostic responses back to the central control unit over the bus line. These diagnostic queries are also sent out over the bus line in the form of a data telegram. This data telegram begins with a start bit, followed by several bits for addressing the addressed data processing unit and information bits. A check bit and a stop bit end the data telegram. If the data telegram contains a deployment command, the bits for the deployment command will be followed by several CRC check bits. The response signal to a diagnostic query has only a few current pulses generated by short-circuiting of the two bus lines in the respective data processing unit. With a response formed in this way, there is the risk that the central control unit cannot assign this response unambiguously to the sending data processing unit and furthermore there might be an error in the response. In addition, no differentiation between different responses is possible with a response having only a few current pulses.
German Patent Application No. 35 06 118 describes a data bus system for motor vehicles in which data telegrams are used for data transmission between the stations connected to the bus, these data telegrams having a control bit region, an information bit region and a check bit region. This publication does not contain any information about special handling of deployment signals for restraint systems in transmission over a bus.
An object of the present invention is to provide a method that permits a reliable allocation of query signals and control signals to data processing units of the bus system and reliable acquisition of monitoring data of data processing units and their respective restraint devices and makes unambiguous assignments of deployment information to the restraint devices.
The object is achieved through the fact that the query signals or control signals and the response signals are data telegrams, all of which have the same frame structure, having a first region with n control bits, a second region with m information bits and a third region with p check bits, and the central control unit enters a deployment command into the region of the m information bits of the data telegram where each data processing unit is allocated at least one bit location of this region, and each individual data processing unit activates the restraint device(s) assigned to it only when the bit intended for it/them has been set.
Processing of the data telegrams in the central control unit and in the data processing units is simplified due to the fact that all data telegrams, both those sent out by the central control unit and those sent back by the data processing units, have the same structure. Various types of response information can be transmitted from the data processing units to the central control unit with a reliable allocation to the sending data processing unit because the response signals are sent back from the data processing units to the central control unit as complete data telegrams.
Advantageous refinements of the present invention are derived from the subordinate claims.
Synchronization bits can be placed in front of the data telegrams for the query signals or control signals, and stop bits can be added at the end of the frame. The synchronization bits facilitate bit clock synchronization in the data processing units.
The control bits in the data telegrams of the query signals or control signals are used to distinguish between different query commands or control commands. The data processing units notify the central control unit by way of the control bits in the data telegrams for response signals whether or not they can correctly execute the query commands or control commands.
Of the m information bits of the data telegrams of the query signals or control signals, a first portion can be used to address the data processing units and a second portion of the m information bits may contain either a selection of one or more memory registers in an addressed data processing unit so that the register content(s) is/are sent back to the central control unit with the response telegram, or the second portion of the m information bits may contain a request to one or more data processing units to execute a certain function. The data processing units enter the queried register contents into the region of their response telegram having m information bits.
The first portion of the m information bits in a query telegram may contain either the address of a single data processing unit selected by the central control unit or the simultaneous addressing of all data processing units connected to the bus line.
Data telegrams with query signals or control signals having a high priority and time urgency (e.g., deployment commands) can be transmitted with a higher signal level and higher bit rate than data telegrams with a lower priority and lower time urgency. This guarantees that at least the signal with the highest priority, namely a deployment command, will always reach the respective data processing unit, even if other data telegrams of a lower priority are being transmitted over the bus line at the same time.